A pipelayer machine is a machine that is specially designed to lay sections of pipe in a trench to create a pipeline. Previously, cranes had been used to raise up pipe sections and lower them into a trench. However, the cranes were not very maneuverable and were commonly modified from cranes designed for other purposes to be used for installing the pipe sections in the trench. Eventually, excavators and crawlers began to be used for installing pipe sections with kits being made and sold to convert an excavator or crawler over for pipe installation duty. Eventually, purpose-made pipelayer machines were designed the sole purpose of which was the installation of pipe section in a pre-made trench.
A pipelayer machine will typically have tracks and a crawler body with an engine. A side boom can extend to one side of the pipelayer machine and the raising and lowering of the side boom is handled by a boom winch. A counterweight assembly is typically provided on an opposite side of the pipelayer machine from the side that the boom is attached to in order to balance out the pipelayer machine and prevent it from tipping when the boom is used to raise and lower a pipe section into a trench.
A hook winch, hook cable and hook are used to pick up and raise a load, such as a section of pipe. The hook winch winds and unwinds the hook cable, which is connected to the hook and is suspended from the end of the boom.
These pipelayer machines are used to lay pipe in a trench by using the tracks to maneuver the pipelayer machine next to a trench the pipe section will be placed in. The hook cable and hook are used with the boom to connect to the pipe section and the hook winch is used to raise the pipe section from the ground. Then, using the boom, the pipelayer machine moves the pipe section over the trench and lowers the pipe section into the trench. Commonly, a number of pipelayer machines will be used at the same time to raise and lower the pipe section into the trench with a number of the pipelayer machines working in unison to raise and lower a single pipe section.
Typically, conventional prior art pipelayer machines will position both the boom winch, which controls raising and lowering the boom, and the hook winch, which raises and lowers the hook suspended from the boom, adjacent to each other on the opposite side of the pipelayer machine that the boom is attached to. This places both winches on the same side of the pipelayer machine that the counterweight assembly is attached to. There are a number of reasons for placing the hook winch on this side of the pipelayer machine, including that having the weight of the hook winch on the opposite side of the pipelayer machine from the side the boom is attached to will help to prevent the pipelayer machine from tipping from the weight of a raised pipe, because the weight of the hook winch will counteract the tipping forces applied to the pipelayer machine by the load suspended from the boom.
While placing the hook winch on the opposite side of the pipelayer machine that the boom is attached to does provide some benefits, there are also problems created by placing the hook winch on this side of the pipelayer machine. With the hook winch provided on the same side of the pipelayer machine as the boom winch, the hook cable typically runs substantially horizontally across the pipelayer machine, between the cab of the pipelayer machine and an engine enclosure of the pipelayer machine, to a fairlead sheave provided on the same side of the pipelayer machine as the boom. After the hook cable passes through the fairlead sheave, it is angled upwards to run to a load block attached to the end of the boom and then down to the hook block and hook. The fairlead sheave prevents the hook cable from getting tangled with the boom or in the tracks of the pipelayer machine, but the fairlead sheave can also cause a high fleet angle on the hook cable which can prevent it from reeving onto the drum of the hook winch properly when the hook winch is winding up the hook cable and raising the hook block and hook.
The fleet angle is the angle of the hook cable coming off/on a winch drum and onto a pulley or a sheave. Looking downwards as the hook cable spools on or off the drum of the hook winch, the fleet angle is the angle that the hook cable varies from being perpendicular to the winch drum. When there is a direct line between the fairlead sheave and the hook winch, the hook cable will be perpendicular to the winch drum and the fleet angle of the hook cable will be 0. However, as the hook cable is wound or unwound around the winch cable and the point where the hook cable winds around the drum moves further to one side or the other of the winch drum, the fleet angle of the hook cable will increase. Typically, the fairlead sheave is positioned so that it is aligned with a centerline of the drum of the hook winch. In this manner, the distance to either end of the hook drum from the centerline (where the fleet angle of the hook cable is 0) is equal; minimizing the fleet angle in both directions. The fleet angle of the hook cable will be large if the ratio of the distance between the centerline of the drum (where the fairlead sheave is aligned) to one of the outside ends of the drum is relatively large and the distance between the hook winch and the fairlead sheave is relatively short. Because the distance between the hook winch and the fairlead sheave is relatively short (just the width of the pipelayer machine), and the fairlead sheave is fixed in one position, the fleet angle of the hook cable can be quite large when it is being wound onto the outer edges of the winch drum in these conventional pipelayer machine designs.
A good fleet angle is between 0.5° to 1.5° of rope angle. If the fleet angle is too large, the hook cable may not reeve on to the drum of the hook winch evenly. In some cases it can even “birdcage” which occurs when the cable has fouled on the drum with overriding turns, locking the hook cable in place on the drum and preventing the hook cable from further unwinding from the hook winch. Birdcaging the hook cable can cause permanent damage to the hook cable by kinking the hook cable and even ruining it so it can no longer be used.
This reeving problem can be increased in pipelayer machines with closed cabs where an operator does not have access to the winch to fix the bird caging without stopping the machine and leaving the cab.
Additionally, the room for the hook cable to run between the cab of the pipelayer machine and the engine enclosure is limited, limiting the length of drum winch that can be used on the hook winch. Using a shorter drum winch can limit how much cable the hook winch can hold and still have enough torque to winch in the cable. The amount of force applied to winching in the cable decreases every time another layer of cable is added to the winch drum.
Additionally, winches are large, heavy, and costly components which are subject to wear and tear during the use of the pipelayer machine. When these winches require maintenance or replacement, it can require significant amounts of time and labor to remove and reinstall the winches on the pipelayer machine.